Telephone-exchange system.



PATENTED NOV. 28, 1905.

H. T. OEDERGREN.

TELEPHONE EXCHANGE SYSTEM.

2 SHEETS-SHEET 1 APPLICATION FILED JAN. 28, 1902.

* 1i; WITNESSES: 40$ 2%? No. 805,901. 7 V PATENTED NOV. 28,1905.

) 'H. T. OBDERGREN. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JAIL-28, 1902.

2 SHEBTS-SHBBT -2- I'NVENTOR BY v 7 ATTOBjNEY UNITED STATES PATENT OFFICE.-

HENRIK THORE CEDERGREN, OF STOOKHQLM, SWEDEN.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

.Patented Nov. 28, 1905.

Application filed. January 28,1902. SarialNol 91,575.

i To all whom it may concern.-

Be it known that I, HENRIK THORE CEDER- Kingdom of Sweden, have invented certain change systems with a central battery supplying current to the transmitting'telephones at the substations, and particularly to that class of these systems having inductive'resistances interposed at the central station between each sistances with a break for the continuous batnew and usefulImprovements in Telephone-- thereof which will be hereinafter described.

In the form of carrying out my invention shown in Fig. 1, A and B denote two substations arranged in the manner common in central-battery systems-i. e. when the telephone is hung upon its switch-hook the signal-bell and a condenser are connected with the linecircuit; but when during conversation the telephone is removed from its hook the telephone receiver and transmitter are connected in series with theline-circuit. From the substations the lines L L lead to the central station. The inductive resistances I 1 and I I respectively, are connected at one end with the line conductors and at the other end with the battery B. Placed behind the resistances are spring-jacks J J P P represent a pair of plugs in the cord-circuit of which the respective condensers K and K are placed in t e manner shown in the drawing. As soon are supplied with such tension.

as a receiving-telephone is removed from its switch-hook a circuit is closed from the battery B through the respective inductive resistances, line, switch-hook, telephone receiver and transmitter. At the other side of the inductive resistances there isno closed circuit for the battery B, as even when two lines are connected together by a pair of cords the condensers inserted in the said cords prevent the passage of continuous current from the battery. 7

As shown in Fig. 1, the spring-jacks arepermanently connected to the'poles of the battery B through the inductive resistances. This may under some circumstances be an inconvenience. If there arises any fault in the field of the spring-jacksfor instance, if the line-contacts come in contact with each otherthebattery will be closed through the jack-field. If, further, one pole of the battery is connected with the earth, as is usually the case, a batterycircuit will also be closed if a jack-line is put in communication with the earth. This inconvenience is, however, overcome by arranging the system as shown in Fig. 2. According to this arrangement the condensers K K have been placed between the inductive resistances and the respective spring-jacks in such a manner that each line contains one condenser. Onepole of the battery is con nected with the earth. The other pole is connected through the inductive resistances I 1 with the line conductors, including the condensers. One pole of the battery being connected with the earth, the conductors 2 4. and adjoined parts have no electric tension, and only the conductors l 3 and adjoined parts The condensers being interposed, however, in the line conductors in front of the spring-jacks and supplied with tension, the latter are not supplied with electric tension from the battery B. As shown in the figure, the strands of the cords are crossed. Although, therefore, only one condenser is interposed in each double line, nevertheless two double lines connected together for conversation always include one condenser in each branch.

- A still more effective manner of keeping the line-contacts of the spring-jacks and the part of the operators set connected thereto free from electric tension is illustrated in Fig. 3. The inductive resistances are here connected only to the outer side of the line. The part of the line leading to the springjacks is connected to a coil 1 or I of the inductive resistances in such amanner that these resistances will, in fact, form transformers for the voice-currents or for the signaling-currents passing through the lines. By this arrangement the spring-jacks will, however,

. have no connection at all with the battery B.

In Figs. 1 and 2 the devices serving to prevent the passing of continuous currents from the battery but allowing the passing of alternating currents have been shown as condensers. able device serving the said purpose can be employed.

Though in the drawings inductive resistances are shown interposed between each pole of the central battery and all the lines, so that two inductive resistances are used for each line, it is obvious to persons skilled in the art that one inductive resistance is suflicient for each line, said resistance being interposed between one pole of the central battery and one branch of the line.

Having now described my invention, what It is, however, obvious that any suit- I claim as new, and desire to secure by Letters Patent, is

A telephone-exchange system of the type specified, having a central battery, conductors which connect the poles of said battery respectively with the two branches of the line conductors, the connecting-points of the said conductors with said branches being situated between the respective springjacks of the lines corresponding substations, inductive resistances interposed between the central battery and the line conductors, plug conductors to unite the spring-jacks of diflerent subscribers, and means for preventing the central-battery current from flowing at any time through any part of the jack-field and cord conductors, substantially as described.

In witness whereof I have hereunto signed my name in the presence of two subscribing witnesses.

HENRIK THORE (JEDERGREN.

Witnesses:

GOTTLIEB PILTZ, K. FR. WINGRANTZ. 

